is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. This process creates a film
of the adsorbate
on the surface of the adsorbent
. This process differs from absorption
, in which a fluid (the absorbate
) is dissolved by or permeates a liquid or solid (the absorbent
), respectively. Adsorption is a surface-based process while absorption involves the whole volume of the material. The term sorption
encompasses both processes, while desorption
is the reverse of it. Adsorption is a surface phenomenon
Increase in the concentration
of a substance at the interface of a condensed
and a liquid or gaseous layer owing
to the operation of surface forces.
Note 1: Adsorption of proteins is of great importance when a material is in contact with blood
or body fluids. In the case of blood, albumin, which is largely predominant
, is generally adsorbed first, and then rearrangements occur in favor of other minor proteins according to surface affinity
against mass law selection (Vroman effect).
Note 2: Adsorbed molecules are those that are resistant to washing with the same solvent
medium in the case of adsorption from solutions. The washing conditions can thus modify
the measurement results, particularly when the interaction energy is low.
Similar to surface tension, adsorption is a consequence of surface energy. In a bulk material
, all the bonding requirements (be they ionic, covalent, or metallic) of the constituent
atoms of the material are filled by other atoms in the material. However, atoms on the surface of the adsorbent are not wholly
surrounded by other adsorbent atoms and therefore can attract adsorbates. The exact nature of the bonding depends on the details of the species involved, but the adsorption process is generally classified as physisorption (characteristic of weak van der Waals forces) or chemisorption (characteristic of covalent bonding). It may also occur due to electrostatic attraction.
Adsorption is present in many natural, physical, biological, and chemical systems, and is widely used in industrial applications such as activated charcoal, capturing and using waste heat to provide cold water for air conditioning and other process requirements (adsorption chillers), synthetic
resins, increase storage capacity of carbide-derived carbons, and water purification. Adsorption, ion exchange, and chromatography are sorption processes in which certain adsorbates are selectively transferred from the fluid phase
to the surface of insoluble, rigid particles suspended in a vessel or packed in a column
. Pharmaceutical industry applications, which use adsorption as a means to prolong neurological exposure to specific drugs or parts thereof, are lesser known.
The word "adsorption" was coined in 1881 by German physicist Heinrich Kayser (1853-1940).